1. Field of the Invention
The present invention relates to a heat pack, and more particularly to a heat pack which is provided with a coil type trigger.
2. Description of the Prior Art
There are provided various kinds of heat packs in accordance with a shape of a trigger which is operated in a supersaturated solution of the heat pack.
As an example of the heat pack, U.S. Pat. No. 5,205,278 discloses a chemical bag warmer comprising a sealed bag which is made of PVC, P.P, P.U. plastic and in which a sodium acetate solution is filled, and a triggering member which is mounted in the sodium acetate and generates an oscillation wave effect in the sodium acetate solution. The triggering member is a disc-shaped member, of which the center portion is a cross-shaped part extended to the edge thereof to divide the center portion into four sectors; each sector has a plurality of fragmental concentric circles to form into a rugged surface, the rugged surface can facilitate the triggering member to bend and vibrate so as to generate the better oscillation wave effect.
Further, U.S. Pat. No. 5,736,110 discloses an activator for initiating crystallization of a supersaturated solution within a flexible container. The activator comprises a flexible screen for immersing in the supersaturated solution within the flexible container. The flexible screen defines a plurality of apertures therein with an activation material being affixed to the screen within the plurality of apertures. Upon flexing of the flexible screen by an operator, the activation material interacts with the screen to initiate crystallization of the supersaturated solution.
In U.S. Pat. No. 4,829,980, there is disclosed a trigger device for a heat pack comprises three helically-coiled, resilient metallic filaments 1,2,3 nested one within the other and of inwardly decreasing diameter, the filament 2 is wound in a sense opposite to that of filaments 1 and 3. Flexing the assembly of nested helices about its longitudinal axes produces a rubbing action between adjacent turns thereof which initiates crystallization. Other devices comprises two nested helices wound in the same sense; a single helix having a pressure plate at one end and an external or internal cap at the other; and a body of randomly convoluted or woven metallic filament.
However, in case of the U.S. Pat. No. 5,205,278 among the constructions of the triggers of the conventional heat packs, as described above, since the triggering member is a flexible metallic piece having the disc-shape, the triggering member may be damaged, when being repeatedly used over a long time. In addition, in case of the flexible screen of the U.S. Pat. No. 5,736,110, such problem may be seriously raised.
Meanwhile, in case of the U.S. Pat. No. 4,829,980, there should be provided a process of nesting a plurality of filaments in order to manufacture the trigger. This makes the manufacturing process complex. Also, in case of the single helix, the single helix has to have a pressure plate at one end and an external or internal cap at the other. Therefore, since there should be provided further process of mounting the pressure plate and cap, there is a difficulty in the manufacturing process.
And in case of the trigger in which two or more filaments are nested, since the plurality of the filaments have to be bent in order to crystallize the supersaturated solution, there is a problem that it is too hard for a user to operate the trigger. In case of the single helix having the pressure plate at one end and the external or internal cap at the other, since the user has to apply a big force to the pressure plate and the cap so as to suppress an elastic force of the filament, it is also difficult to operate the trigger.